Self Contained Breathing Apparatus Modular Control System

ABSTRACT

The claim over prior art is for an approach to an electronically controlled or electronically monitored breathing system that represents an improvement in electrical reliability, manufacturing cost and efficiency, user maintenance, system reliability, user cost and maintenance. These improvements are accomplished by placing the major electronic, mechanical and electromechanical control elements and sensor components in a single replaceable module.

CROSS REFERENCE TO RELATED APPLICATION(S)

The present utility patent application claims benefit of U.S.Provisional Application Ser. No. 60/605,561, filed Aug. 30, 2004 in thenames of the present applicants, subject matter of which is incorporateherewith by reference.

FIELD OF THE INVENTION

The present invention relates: generally to respiratory methods ordevices supplying respiratory gas under positive or ambient pressure;more specifically to electric control means for the supply ofrespiratory gas under positive or ambient pressure; most particularly toelectric control means for the supply of respiratory gas under positiveor ambient pressure by a respiratory method or device utilizing meansfor sensing partial pressure of a gas constituent.

BACKGROUND OF THE INVENTION

Breathing devices like Closed and Semi Closed Circuit Rebreathers andother closed loop breathing systems rely on electronic control systemsto monitor the oxygen level through the use of oxygen sensors and toprocess the system information to determine if a solenoid or valve needsto be opened in order to add more oxygen into the breathing system. Upto now, this has involved a complicated and interconnected array ofcomponents to accomplish this task. The batteries, control electronics,sensors, and gas control devices all must be connected with cables andvarying levels of connectors. Breathing systems to date have neitherconsidered these subcomponents as a complete system nor have the controlsystems in general been considered as an integral part of the systemdesign for the rebreather itself. The resultant breathing system designshave therefore treated the control system as both a separate system fromthe rebreather and have considered the individual components of theelectronic control and sensing system as generally separate designelements. All of the control system subcomponents and parts havemaintenance and reliability issues that either requires regularmaintenance or possible replacement. All of the necessary electronic andmechanical interconnects between these components represent points offailure as well as increases assembly time, maintenance, and systemcost.

All breathing device control systems require maintenance and haveattendant diagnosis and or possible replacement issues. Successfuldiagnosis and replacement can be as easy as replacing a battery orsensor to as complicated as sending the entire breathing unit in for afactory trained technician to diagnose and service. The latter optioncomes at an additional cost of significant down time. On current,non-modular systems, parts can be very difficult to remove and replace;especially in the field or on short notice. A significant array ofavailable spare parts is therefore necessary to be able to repair anycontrol related failure in most breathing systems.

Manufacturer upgrades to the control system typically consists ofsending the entire unit or a significant portion thereof back forretrofitting. This is both costly and inefficient.

In rebreathing systems, a popular implementation has been that theseparate pieces have been combined into a single large “head” whichcomprises the entire top assembly of a rebreather. This “head” typicallyincluding breathing hose mounts, scrubber and breathing bag supplypaths, some of the electronics, sensors and or the gas injectionsolenoid. The “head” therefore, is a substantially sized and pricedpiece of the breathing system with a great deal more functionality andcost than just the control subsystem and includes a great deal ofmechanically oriented parts and mountings which are not as likely tofail or need replacement as the control and sensing subsystem. Withinthe “head”, the components of the control and sensing subsystem arestill treated as individual components with all the attendantdifficulties remaining concerning cost and reliability.

SUMMARY OF THE INVENTION

The invention is summarized by considering that manufacturers and usersof breathing systems are concerned with costs, reliability maintenance,and serviceability of these breathing systems. Claims are made forClosed and Semi Closed configurations of rebreathing systems thatminimize electronic and mechanical failures by incorporating themicrocontroller and associated electronics, measurement subsystemelectronics, input and output cabling, connectors, gas control solenoidsand software into a single removable module. Claims are made for theintegration of the low pressure Oxygen, intra-stage Oxygen pressure,high pressure gas supply and ambient barometric pressure measurementsubsystems and for the integration of the controller power supply.Claims are also made for wireless transmission of the data to and fromthe sensors and or measurement subsystems and to and from the userinterface via the display subsystems. A claim is also made for theintegration of a Personal Alert Safety Subsystem into the modularcontroller. This single module approach offers significant benefits inmanufacturability, reliability, serviceability and maintenance. Theadditional benefit of reducing the technical knowledge required toperform maintenance and replacement tasks is also realized.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings which are incorporated in and form a part ofthe specification illustrate preferred embodiments of the presentinvention and, together with a description, serve to explain theprinciples of the invention. In the drawings:

FIG. 1 is a picture of a complete electronically controlled mixed gasclosed circuit rebreather.

FIG. 2 is a drawing of one example of a modular controller assembly.

FIG. 3 is a front view drawing of one example of the interface betweenthe modular controller and scrubber assembly.

FIG. 4 is a ¾ view drawing of one example of the interface between themodular controller and scrubber assembly.

FIG. 5 is a schematic representation of a mixed gas closed circuitrebreather.

FIG. 6 is a schematic block diagram of the example modular controller.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

For purposes of example, this preferred embodiment is demonstrated on aclosed circuit breathing system known as an MK15 style electronicallycontrolled mixed gas closed circuit underwater rebreather (FIG. 1) whichhas had its scrubber housing (FIGS. 3 and 4) and external case modifiedto accept the modular controller assembly (FIG. 2).

This example describes a mechanical module which serves as a containmentfor the electronic, mechanical and sensor components of the controlsystem as referenced in claim 1. Other configurations as outlined in theclaims are possible and practical such as remote, non-module containedsensors or use in other types of breathing systems.

The modularized control system for this example is a microcontrollerbased system with the hardware and software necessary to provide theability to sense the partial pressure of Oxygen within a breathing loopusing standard Oxygen partial pressure sensors such as Teledyne R22Ds[available from Oxycheq.com]. (2, 4 and 6). The controller (22) andassociated firmware also has the ability to control the injection of lowpressure (standard SCUBA interstage pressures of between 165 psi and 95psi) Oxygen with a solenoid (62) such as the Wattmiser model by SnapTite[2W12w-1NB-V0A4 distributed by FasanAll] into a breathing loop.

The mechanical module (22) is made of Delrin and machined in such a wayas to create an o-ring gland (20) on one end to facilitate a bore-seal(28) into the breathing loop area of the rebreather scrubber canisterhousing (24). The inside of this module is machined such that a printedcircuit board may be placed inside in a manner which allowsencapsulation by a potting material, such as Epic S7285. Towards the endof the module (22), which is placed into the rebreather scrubbercanister housing (24), are gas path and access holes sufficient toprovide for the removal and replacement of the gas sensors (2, 4, and 6)as well as providing a vent port (12) connected to the output port ofthe gas solenoid (62).

There is a low pressure (less than 200 psi), O₂ cleaned, gas fittingmounted on the inside of the module (22). The inside of the module (22)at the point of the gas entry (14) is machined such that a gas-tube barbmay be fitted on the inside of the module (22) and provide a lowpressure gas tube fitting to the input port of the gas solenoid (62).

An isolation barrier is formed by the isolation gasket (8) machined intothe controller module (22) to provide separation between the inhalationand exhalation sections of the scrubber housing (24).

A printed circuit board (PCB) is manufactured (using industry standardprinted circuit board techniques such as created with ORCADCapture/Layout and ordered through PCBPRO.com) which is shaped toconform to the area defined inside the module (22). The PCB provides ameans for mechanical placement and circuit communications and controlpaths between the elements of the control subsystem including the gascontrol solenoid (62) and said Oxygen sensors (2, 4 and 6). The PCB alsoprovides for the means of electrical interconnection to waterproofbulkhead protected cables (10 and 16) which are mounted on the side ofthe module (22). These cables, (10 and 16), provide a signalinterconnect for the user worn primary (38) and secondary (42) displaydevices.

The top of the module (22) provides a separate waterproof compartment(18) for the installation of a standard alkaline 9 volt battery (18)which provides power to the plurality of control system components.

The control subsystem is defined by several main components; amicroprocessor (90) such as the Motorola MC68HC908JL8CDW (FIG. 3-13)[MC68HC908JL8CDW-ND as ordered through Digikey distribution, anacquisition and measurement subsystem consisting of a multiplexer aMaxim 8:1 analog multiplexer such as a MAX4783EUE [as ordered directfrom Maxim-IC.com] (88, 96) and a high resolution (34 bit)Analog-to-Digital converter such as a Maxim MAX32555ETL [as ordereddirect from Maxim-IC.com] (92 and 98), a power supply consisting of astandard 9 v battery (18) and standard voltage regulating circuitry(100) such as a Toko 3.3 volt regulator TK73733SCL [TK73733SCL-ND asordered through Digikey Distribution], a solenoid control subsystemconsisting of a solenoid firing circuit (94) and a solenoid Wattmisermodel by SnapTite [2W12w-1NB-V0A4 distributed by FasanAll] (62), andsensors and feedback devices consisting of sensors and associatedconditioning electronics for sensors (2, 4, 6, 112). Input channels andassociated software is provided as necessary for other implementationsof additional functional configurations of the modular control systemsuch as external temperature (116), body temperature (114), O₂ supplypressure (110), solenoid current sense (108), diluent supply pressure(106), biometric sensors (104), O₂ intra-stage pressure sensors (102),and ambient pressure (120).

The circuit components are connected together using a Printed CircuitBoard (PCB) using industry standard printed circuit board techniquessuch as created with ORCAD Capture/Layout such that the shape conformsas necessary to fit the space provided in the module.

In this example the measurement system for the secondary monitor (96,98) is powered independently by the secondary display so as to decreasethe likelihood of linked failures between the primary and secondarysystem. The acquisition and measurement of the Oxygen sensors (2, 4 and6) are performed by the secondary display unit (42) via direct controlof the multiplexer (96) and ADC (98) by the microcontroller containedwithin the secondary display unit (42).

The sensors of the system are connected to the multiplexer (88). Theoutput of the multiplexer (88) is in turn connected to the ADC (92). Thedigital controls of both the analog multiplexer (88) and the ADC (92)are connected to the microprocessor as is the solenoid firing circuit(94) (solid state relay such as IR PVN012) which fires the gas additionsolenoid (62).

The primary control system microprocessor (90) has sufficient inputs andoutputs such that the embodied firmware may calculate all appropriateconsiderations into a sufficiently accurate level of partial pressure ofOxygen within the breathing loop for and during human inhalation andexhalation.

The firmware will then make a determination as to the need for additionof Oxygen by the module (22) into the breathing loop (24). If necessary,the firmware in the microprocessor (90) will utilize the solenoidcontrol subsystem (94) to cause the solenoid (62) to open for asufficiently long duration such that sufficient Oxygen is added to thebreathing system to maintain the desired level of Oxygen within thebreathing system.

Additional firmware is embodied such that the user primary displaydevice (38) may inform the user of low battery and other errorconditions as well as of the level of Oxygen in the system. The controlsubsystem is enabled to turn on via action of a pressure switch (110)acting on the systems intermediate Oxygen pressure as detected in thegas flow path (14).

The firmware for accomplishing the above tasks is written in assemblylanguage and downloaded using standard industry programming devicesspecific for the processor of choice. The firmware is structured in anumber of extensible code spaces divided between interrupt driven timedstructures and loop driven structures. The time driven structuresprovide timed standard code spaces with the time intervals occurring at200 us, 10 ms, 50 ms, 100 ms, 1 sec, 10 sec, 1 minute, and 1 hour. Theloop driven structures are divided between a Primary Loop and twoRound-Robin Loop spaces. All code spaces in the Primary Loop space areexecuted through the entire loop space as frequently as possible butwithout regard to exact time. One of the Round-Robin code spaces isexecuted once per pass of the Primary Loop code space and is used forless time critical applications.

The overall code structure is divided between 3 levels of functionsdealing with Core, Standardized Support, and Application Specific codefunctions—all code in those spaces executing in one of the abovementioned timed or loop driven code spaces. Each of the measurementfunctions is carried out on a timed and table driven process whichaccumulates one set of measurements every 50 ms. As each measurement isselected, the multiplexer is set to pass that measurement parameterthrough to the ADC (Analog to Digital Converter), the ADC is theninstructed to make the measurement which is then stored in RAM in themicroprocessor. This is a Round-Robin process initiated by a timer inthe 50 ms code space. Execution Flags are set as each measurement istaken to cause an additional Round-Robin process to execute whichaverages the value of each measurement and determines if the measurementis valid in terms of ADC functionality.

The PO₂ evaluation consists of a number of steps. These steps are tofirst acquire the raw ADC readings. These are then averaged and turnedinto voltage readings for each sensor. These are stored and alsotranslated via the calibration variables to PO₂ values. The PO₂ andmillivolt values are examined for each sensor for validity and low levelerror bits are set accordingly for each sensor as required. For thesensors that are determined to have valid readings, they are averagedtogether and then evaluated individually relative to the averaged valueto determine if it is in fact valid to include each sensor in theaverage. Sensors that are too far apart must have different algorithmsapplied to determine the most likely true PO₂ level. Appropriate Highand Low Level errors are set depending both on the relationship of thesensors to each other as well as the resultant PO₂ determination.

History Transmission: A generic core based queue management system isused to handle multiple RS232 transmission requests. This system managesthe task of transmitting a block of data byte by byte and does notrequire any other involvement from the applications code except toprovide a request flag set and to provide the necessary data pointers tothe block of data. Once the transfer is complete, the system sets a datatransfer complete flag that is specific to each data request to enableany action that is waiting on that specific transfer.

Watchdog Timer: This is a firmware driven timer that exists to validatethe selection and execution of either the Diagnostic Mode or the ActiveMode. This is meant to monitor the system for major errors in internalprogram flow has not engaged one of the two major wakeup modes. Iftriggered and the unit is the Master, it will declare a high level errorand attempt to failover to the lower processor. If the lower processordoes not exist, the Active Mode will attempt to be forced.

Low Battery Detection: Both battery inputs have an ADC request generatedonce per 100 ms. This is averaged in a Round Robin routine and thentranslated from the resistor divider output level into true batteryvoltage levels. These levels are then compared against thresholds forerror conditions and appropriate flags are set. This is a Low Levelerror since even if the battery is too low to fire the solenoid, therewill be no High Level error generated except as the PO₂ reaches adangerously low level of 0.18PO₂.

Fault System: The fault system consists of a High and Low level trackingsystem. Each specific error is generated by individual independentlyoperating routines. These errors are usually in bytes or flags specificto each area of operation. Once per second, these errors are translatedinto High and Low Level error bytes that are then checked by the Activeand Diagnostic Mode routines.

In addition to the core structure, the Generic Core provides a number ofprocesses to support the applications code. These consist of the SPI andRS232 request queue management and drivers for external communications,multiple pushbutton debounce and state management, internal ADC support,and Math routines.

Sensor Data Management: Sensor data management is the core criticalprocess of the controller. This is the process that determines the besttruth to be obtained from 3 channels and the connected 3 sensorsregarding the level of Oxygen in the monitored breathing loop. At firstglance, this is not a complicated process. Most implementations ofbreathing loop controllers will address determining the “correct” Oxygenlevel from three good sensors with one of several philosophies—Thedifferences that those philosophies produce in reported PO₂ levels arenegligible. Due to the malleability of the output of fuel cell basedOxygen sensor cells, it is a standard practice to detect and allow for asensor to be out of range of the other sensors by averaging theremaining two sensors. The definition of “out of range” is arbitrary anddifferences in out of range definitions do not produce significantlydifferent PO₂ results. These standard approaches produce acceptableresults under these limited circumstances of predominately functionalsensors and measurement systems.

In addition, it is common to apply the same rules for Oxygen leveldetermination for all purposes such as Solenoid Control, OperatorDisplay, Alarm Control, and Calibration Condition. While applying thesame rules for determining Oxygen levels for these purposes makes sensewhen everything is predominately functional, as conditions degrade forwhatever reason, the requirements of each purpose may diverge and oneOxygen Level determination process will no longer produce optimumresults. As an example, the situation of all three sensors producinggreatly divergent readings results in different demands from the abovelisted processes: Operator O₂ Display has a mandate to display the knownPO₂ level but in this case, there is no means of determining an actualPO₂ level and the most appropriate display is to indicate an errorcondition. The Solenoid Control process has the primary goal ofmaintaining a defined setpoint. A secondary goal is to behave in amanner most likely to keep the operator alive regardless of theinexactness of the precise Oxygen level. In this case, since it is morelikely that sensors are falsely low due to the chemistry of theirconstruction; the averaging of the two highest sensors is most likely toproduce an Oxygen level that may not be accurate but will remain withina livable Oxygen level. The Alarm Control's job is to indicate when itis likely that the Oxygen level has reached a dangerous level. In thiscase, since it is not known which if any of the sensors are accurate, itis necessary and desirable to err on the conservative side more so thanthe Solenoid Control system. A meaningful system would be to allow thealarm for O₂ dangerously high to be run by the highest sensor alonesince that is the most likely to be accurate due to the most commoncauses of O₂ failure. On the other hand, the alarm for O₂ dangerouslylow conditions would run off the average of the two lowest sensors. Thisis due to the most likely failure mode being to produce a output lowerthan the actual Oxygen level. The average of the two lowest sensors willproduce an Alarm Level that will functionally catch an actualdangerously low O₂ level if there is any nominal relationship betweenthe sensor outputs and actual O₂ levels, there is a much better chancethat these rules under this circumstance will produce far moremeaningful results than simply using the same approach for all purposes.These rules change a number of times depending on both what the sensorsare outputting relative to one another then also change again whenadditional error sources are taken into account such as wire breaks,failures in connectors or measurement electronics, etc.

The result of all this is a dual level matrix of rules. The first levelassociates the 4 main processes (Display, Solenoid, Alarm, andCalibration Condition) to the number of sensors that are producinginformation that is assessed as meaningful (3 channels, 2 channels, 1channel, no channels). In each of these 16 rule areas, the output of theexisting sensors are also assessed in a matrix determining the explicitrules for all of the circumstances of how close or not the sensors aretracking each other (3 close, 2 close, none close) for each of the 4main processes listed above.

The exact nature of an expanded rule generation for different purposesmay change depending on the philosophies of the designers and/or uponthe explicit operational or design goals of the system but the elementsof accessing different processes with different rules makes significantcontributions to the ability to maintain mission capable system in theevent of system failures or functional degradations. As in the exampleabove, it is possible to function with one simple rule for all purposes(such as use the middle sensor), it may not always produce as meaningfula result under all possible circumstances.

1. A modular, self-contained, removable control subsystem for abreathing device comprising a microcontroller, measurement electronics,input/output cabling, connectors, gas control solenoids, gasconnections, and software for the purpose of controlling gas addition tothe breathing device.
 2. The modular control system of claim 1comprising a low pressure Oxygen measurement subsystem.
 3. The modularcontrol system of claim 1 comprising a mid (intra-stage) pressure Oxygenmeasurement subsystem.
 4. The modular control system of claim 1comprising a high pressure gas measurement subsystem.
 5. The modularcontrol system of claim 1 comprising a system power supply.
 6. Themodular control system of claim 1 comprising a Barometric sensor(s) anda pressure sensing measurement subsystem.
 7. The modular control systemof claim 1 comprising wireless transceiver(s) to communicate data to andfrom the breathing system measurement devices.
 8. The modular controlsystem of claim 1 comprising a wireless transceiver(s) to communicatedata between the module and display/input devices.
 9. The modularcontrol system of claim 1 comprising a Personal Alert Safety System(PASS) subsystem.